Interference reducing radio receiver



R. B. BuLLocK 2,468,030 INTERFERENCE REDUCING RADIO RECEIVER 2 Shexets-Sheet 1 April 26, 1949.

Filed Feb.. 23, 1945 April 26, 1949. R. B. BuLLoK INTERFERENCE-REDUCING RADIO RECEIVER 2 Sheets-Sheet 2 .DEW

Patented pr. 26, 1949 IN TEREERENC E' REDUCING RADIO RE CEIVER Roy B. Bullock, Oshkosh, Wis., assignor to Ira Milton Jones, trustee, Milwaukee, Wis.

Application February 23, 1945, Serial No. 579,344

(Cl. Z50-20) 6 Claims.

l This invention relates to av method of and apparatus for receiving transmitted radio waves.

The object of this invention is to accomplishV radio' reception free from the effects of static or interference.

It is a commonly known and accepted fact that since the inception of radio it has been the desire and the ambition of engineers, radio technicians, and others, to iind a practical and practicable means for eliminating atmospherics or man-made interference. It has further been the hope of everyone who listens to radio communications that the elimination of such interference would be accomplished. This hope has been based upon practical need, as Well as upon the wish for interference free program reception; for the elimination of interference would effect not only a better vbut a far more extendedV purpose.

However, authorities agree that heretofore no one has succeeded in achieving radio reception limitations. By virtue of its need for a Wide band' it has been of necessityV ruled out of the standard broadcast spectrum and assigned to a high frequency Zone. The characteristics of the high frequency spectrum in which FM now generally operates restrict the eective service area of a transmitter broadcasting at such frequencies. Thus FM kas now used has a relatively small service area, the radius of which usually does not exceed sixty miles.

Therefore, in order to cover any large areaA effectively and so make FM transmission and reception practicable and practical the establishment of numerous broadcast and/or relay stations is necessary. To do so involves tremendous initial expenditures andcontinued correspondingly high operating and maintenance costs. Furthermore, standard radio receiving equipment forl use on standard broadcasting bands is incapable of receiving frequency modulated broadcasts and therefore new receiving equipment is necessary.

This invention requires no change from present day amplitude-'modulated broadcasting, which. is considered the most advantageous form of radio transmission. Thezentire purpose of the invention is effected in the receiver. Thus the vast expenditure which would be entailed by any plan aifecting the transmitter is obviated.

Moreover, the method of this invention permits using either the superheterodyne or the tuned radio frequency type of receiver circuit; and, if desired, the apparatus necessary to embody this invention in a receiver may be constructed as a separate unit for connection to a receiver already in use.

As will appear more fully hereinafter this invention is predicated upon the fact that insofar as present knowledge is concerned, static and/or' other interference, either atmospherics o-r manmade, will appear as only a single side band at' any given frequency. Thus, if the transmission is of the double side band amplitude modulated type, and if interference side bands are present, an inequality exists as to the number of voice sidebands and interference side bands for any given frequency accepted by the receiver, and this condition is utilized by this invention to eliminate the interference.

It is, therefore, more specifically an object of* this invention to provide a method and apparatus for receiving double side band amplitude modulated radio waves so as to eliminate the effect of atmospherics or man-made interference; but it must be understood, of course, that any static ori interference which is 'coherently relatedin the' form of double side-band amplitude modulationto the carrier of the station to which the radio receiver is tuned will not be affected.

With the above and other objects in View,

-which will appear as the description proceeds,

this invention resides in the novel method and sequence of operation as well as the novelconstruction, combination and arrangement of parts' substantially as hereinafter described, and more particularly defined by the appended claims, itr being understood that such changes in the precise embodiment of the herein disclosed inventionl may be made as come within the scope of the' claims.

The accompanying drawings illustrate twol complete examples of the method and physical embodiment of the invention, propounded and constructed in accordance with the besty modesso far devised for the practical application of' the principles thereof, and in which:

Figure 1 diagrammatically illustrates an appli-r cation of this invention as applied to a superheterodyne type of receiver; and

Figure 2 diagrammatically illustrates an application of this invention as applied to the tuned radio frequency type of receiver.

Before specifically expounding the embodiments of the invention diagrammatically shown in the drawings, it will be helpful to consider thenature of the transmitted Wave in conventionalulation.

amplitude modulated radio transmission. As is well known to those skilled in the art, the intelligence to be transmitted is rst translated into its electrical counterpart. The frequency of the wave thus produced is that of the original intelligence, so that in the transmission of sound (speech, music, etc.) it is at audio frequency and may be termed the voice Wave. This voice wave is used to modulate a radio frequency carrier wave which in turn is radiated from the broadcasting transmitter.

The modulated radio frequency carrier wave contains components of at least three radio frequencies, namely, the frequency of the original carrier wave, and the sum and difference of the original carrier frequen-cy and the modulation or voice wave frequency.

These additional frequencies are called the side band frequencies, while the original radio frequency component is called the carrier. For eX- ample, assume that the carrier frequency of a transmitter is 600 kc. and that it is modulated by a5000 cycle audio signal. The sum and difference frequencies thus are 605 kc. and 595 kc., respectively.

. In order for these three frequencies to create the desired signal envelope they must bear the well-known phase and amplitude relationship to each other that gives rise to pure amplitude modulation.

The existence of the two side bands, which hereinafter will be referred to as voice side bands, is important to this invention. Static or other interference capable of affecting radio reception and not coherently related-in the form of double side-band amplitude modulationtc the carrier of the selected transmitting station is manifested in the receiver and before detection as a single frequency band for any given frequency of its audio characteristic inasmuch as there is no modulation involved in its creation.

Another observation important to this invention is that such interference will produce an audio frequency wave upon detection or demod- Thus by combining the audio component of each received interference frequency band which for convenience will be designated hereinafter as the interference side-band notwithstanding the connotation of duplication which the term side-band has with an identical audio component derived in some suitable Way and which is 180 out of phase therewith, it is possible to cancel the effect of the static or interference.

Attention is now specifically directed to Figure 1 of the drawings which illustrates in block dia.- gram an application of this invention to a superheterodyne type of receiver. As here shown the receiver proper comprises an antenna 5 connected to an RF amplifier and frequency converter unit 6. The output of this unit 6 is fed into a conventional I. F. amplifier unit 'I and from there t0 a detector 0r demodulator 8. The output of the detector or demodulator ordinarily is fed directly to an audio frequency amplifier unit 9, but for the purpose of this invention a mixer stage or unit IEB is interposed between the units 8 and 9. The output of the audio frequency amplifier 9, of course, is fed to the conventional speaker Il.

These component parts which make up the conventional superheterodyne receiver have been designated in Figure 1 as channel #1, but as will appear hereinafter, this channel #l more specifically terminates at the input of the detector or demodulator unit 8.

The output of the R. F. amplifier and frequency converter unit 6, in addition to being fed into the amplifier '1, is fed into another channel designated channel #2 and comprising an I. F. amplier unit I2 which is a counterpart of the unit 1. The output of the I. F. amplifier I2 is fed into a mixer unit I3 which feeds a detector or demodulator unit I4. This detector or demodulator I4 is connected with the mixer unit I0 in channel #l so that ythe demodulated outputs of the two channels may be combined.

The incoming modulated carrier, together with any accompanying interference side bands, in addition to being fed into the channels #l and #2 is also fed into a detector or demodulator and phase inverter I5 the output of which is used to modulate a locally produced carrier emanating from an oscillator I6, this modulation taking place in a modulator unit I'I. The oscillator produces a carrier wave hereinafter referred to as the locally produced or provided carrier which is a duplicate of the carrier component of the modulated c-arrier progressing through channels #l and #2.

Assurance that the output of the oscillator will be this desired duplicate is provided by a sharplyL tuned amplifier unit IB connected between the oscillator and the output of the R. F. amplifier and frequency converter unit 6. Through the provision of this sharply tuned amplifier the output of the oscillator is constrained to the frequency and phase characteristics of the carrier component of the modulated carrier emanating from the R. F. amplifier and frequency converter and fed into the I. F. amplifiers 'I and I2.

As depicted by the arrows in the legends applied to the block diagram, the phase (or polarity) of the voice and interference side bands as well as the R. F. carrier is the same in the I. F. amplifiers 'I and I2 and the input of the detector or demodulator I5. However, due to the manner in which the detector and phase inverter I5 is arranged and connected the phase of the voice audio and interference audio components coming from the demodulator I5- is inverted. For perfect results this phase inversion must be complete; that is, the voice audio and interference audio, which constitute the product of the demodulator I5, must be out of phase with the side bands fed into the mixer unit I3 from the I. F. amplifier I2.

In View of the phase inversion which characterizes the product of the detector unit I5, the polarity of the two voice side bands and the two interference side bandsall in the output of the modulator unit I'I-is opposite to the polarity of the two voice side bands and the single interference side band in channel #2. This phase opposition, or opposite polarity relationship between the side bands in the output of the modulator I'I and those in channel #2, is depicted in Figure 1 by the three side band labeled arrows shown above the I. F. amplifier unit I2, which point to the right, and the four side band labeled arrows shown to the right of the modulator unit I1, which point to the left. The carrier component of the output of the modulator unit I'I, however, is in phase with the carrier in channels #1 and #2 as depicted by the arrows labeled 1. F. carrier and carrier (I. F.) all of which point to the right.

The frequency and amplitude of the output of thel modulator I'I is identical with that of the amplifier I2, this condition being assured by an equalization indicator I9 connected between the amplifier I2V and the modulator I1.

This. equalization indicator I9f may.l employvv cathode ray tube or-l an electron ray tube, either` ofrwhich can be used with appropriate well knowncircuits to serve as a means for tuning adjustment and equalization between the outputs of the I. F. amplifier I2Vand modulator I'I.

The combination of the locally produced modulatedzcarrier (the outputofthe modulator unity Ia'I) with the received modulated carrier prov gressing through channel #2 in the4 mixer unit I3results in cancellationl of the voice side bands and the cancellation of one of the two interfer-V ence side bands of the modulated locally p ro.-V duced carrier by the singleinterferenceside band inichannel #2 as depictedin the legend applied tothe mixer unit block I3. The combining of these two modulated carriers thus leaves a care rier which is the sum of the twocarrier components of the combined modulated carriers and one interferencel side band which is Opposite in phase to the interference side band of c hannel #1. It is this wave combination, namely carrier and interference side band, whichis fed intothe detector or demodulator unit I4 which eliminates the carrier.

The output of the deniodulator unit I4 which is fed into the mixer unit Ill is only interference audio out of phase with the interference audio leaving the detector or demodulator unit 8. Consequently, by mixing or combining the outputs of the detectors or demodulators 8 and I4 the out-of-phase interference audio components cancel each other leaving theinterference-free voice audio to pass on to the audio frequency amplifier.

As will be readily apparent to those skilled in the art, the use of the superheterodyne circuit has the advantage of facilitatingl the maintenance of the necessary synchronism between the' carrier Wave locally produced by the oscillator I6 and the carrier component of the modulated carrier progressing through the two I. F. ampliers 'I and I2.

It is also possible, as shown in Figure 2, to adapt this invention to the conventional 'TRF type of receiver. In this case channel #l com; prises successive R.. F. amplilier units` 2D and,2I, a detector or demodulator 22, av mixer unit 23, and an audio amplier 24. Channel #2 comprises an R. F. amplifier 25 which is a duplicate of the amplifier unit 2 I.

The incoming energy received by the antenna is rst amplified by the R. F. amplifier unit and is then fed into the R. F. amplifiers 2 I and and. also into a selective filter unit 26. This selective filter unit is constructed so as to eliminate all side bands from the energy fedinto it so that its output consists of only the carrier component of the received modulated carrier. Thus the selective lter unit 2li serves the function of the oscillator in the previously described embodiment of the invention in that it locally provides a carriei` having the same frequency and phase characteristics as the carrier component of the modulated carrier progressing through channels #l and #2, The output of the selective filter unit 26 is brought to an adequate amplitude in a conventional amplifier unitk 21 theoutput of which is fed into the modulator II.

The locally provided carrier must be; modulated by the voice audio and interference audio components of the energy progressing through the channels #1 and #2,/ but any means whereby thisA is accomplished can: be employed. In the embodiment of the invention illustrated inv Figure .1 the modulation frequencies; were the product' of; thev demodulator unit. la The Same result can be achievedbv extracting voice audio and,

interference audio components from the modulated carrier progressing through channel #1- at4 the output of the-detector or demodulator unit 22 as shown in Figure 2. Thisoutput preferably should be amplifiedvk as by an amplifier unit 2:8` before being fed intovthe modulator I1, but either.` inthey ampliier unit 28 or some suitable adjunct the phaseY of the voice audio and interference audio components-fed into the modulator must be inverted. v

The modulation o f the locally provided carrier in the modulator unit I'I, the combination of the product of` this modulation with the output of channel #2, the demodulation of the combined result and the combination of the demodulated outputs of channels #l and #2 in the mixer unit 23, all proceeds ashas been described in connection with the embodimentof the invention illustrated in Figure l'.

From the foregoing description, takenin con,-

nection with the accompanying drawings, it will be readily apparent to lthose skilled in the art,

. that this invention provides means for completely eliminatingv the effect of atmospherics or man1 made interference in the reception of double side band amplitude modulatedradio waves; that the achievement of this objective entails no modication'of present day amplitude modulated broadcasting practice except that in all instances both sidey bands of the modulated carrier must be transmitted; that being able to eliminate any disturbance which is represented in the pattern of theincoming energyr as a single side band for any given frequency of, its audio component, the invention permits an overlap of adjacent broadcast channels, thus (if desired) allowing the-present 10 kc. channels to be widened to encompass more nearly the full range ofaudible frequencies and thereby achievehigher fidelity without re- Vision of present channel allocations; that the extent of the permitted overlap is great enough to allow for a desirable widening of the 10 kc. channels and at the same time make possible an increase inthe number of broadcast stationswith.- in the present broadcast band; and further, that utilization of the invention is not limited to any prescribedtype of receiver.

What I claim as my invention is:

1. A method of receiving double side band amplitude modulated radiovwaves so as to eliminate the eifect of linterference manifested as a single .side band frequency for any interference audio component, and which is not coherently relatedin the form of doubleside-band amplitude modulation-to the carrier of the selected transmission which comprises: simultaneously amplifying the received modulated carrier and accompanying Asingle side band (for each frequency) of the in.-

terference in two separate amplifying channels; extracting voice audio and interference audio components of the receivedenergy; inverting the phase of the voice audio and interference audio .components so extracted; providing a carrier which is aduplicateof the carrier component of the modulated carrier progressing through each of the two amplifying channels; locally modulating said provided carrier with the phase inverted voice audio and interference audio components of the received energy so that the two voice side bands. and two interference side bands resulting from said ,modulation are opposite in phase to `the voice and -single interference side bands in one of, saidtwo channels.; combining the locally modulated carrier with the received modulated carrier and single interference side band in said mentioned one of the two amplifying channels so that the voice side bands of said combined modulated carriers are cancelled and the single interference side band of said mentioned channel cancels one of the interference side bands of the locally modulated carrier leaving the sum of the combined carriers and one interference side band as the output of said mentioned one of the two channels; demodulating the outputs of the two amplifying channels so as to provide interference audio and voice audio in one channel and only interference audio in the other channel; and combining the products of said last named demodulations with the interference audio of one channel opposite in phase to that of the other channel.

2. A method of receiving double side band amplitude modulated radio waves so as to eliminate the effect of interference manifested as a single side band frequency for any interferen-ce audio component, and which is not coherently relatedin the form of double side-band amplitude modulation-to the carrier of the selected transmission which comprises: simultaneously amplifying the received modulated carrier and accompanying single side band (for each frequency) of the interference in two separate amplifying channels; extracting voice audio and interference audio components of the received energy; inverting the phase of said extracted voice audio and interference audio components, locally producing a carrier which is a duplicate of the carrier component of the modulated carrier progressing through each of the two amplifying channels; modulating said locally produced carrier with the phase inverted voice audio and interference audio components so that the two voice side bands and two interference side bands resulting from the modulation are opposite in phase to the two voice and single interference side bands in one of said two channels; combining the modulated locally produced carrier with the received modulated carrier and single interference side band in said mentioned one of the two amplifying channels whereby the voice side bands of said combined modulated carriers are cancelled and the single interference side band of said mentioned channel cancels one of the interference side bands of lthe modulated locally produced carrier leaving the sum of the combined carriers and one interference side band as the output of said mentioned one of the two channels; demodulating the outputs of the two amplifying channels so as to provide interference audio and voice audio in one channel and only interference audio in the other channel; and combining the products of said last named demodulations with the interference audio of one channel opposite in phase to that of the other channel- 3. A method of receiving double side band amplitude modulated radio waves so as to eliminate the effect of interference manifested as a single side band frequency for any interference audio component, and which is not coherently relatedin the form of double side-band amplitude modulation-to the carrier of the selected transmission which comprises: selectively filtering a portion of the energy of the received modulated carrier and accompanying single side band (for each frequency) of the interference to remove all side bands from the carrier; simultaneously amplifying the remainder of the energy of the received modulated carrier 1n a first amplifying channel and a second amplifying channel; extracting voice audio and interference audio components from the rst amplifying channel; inverting the phase of the extracted voice audio and interference audio components, locally modulating the sideband-free carrier (obtained through the selective filtering) with the phase-inverted voice audio and interference audio components so that the two voice side bands and two interference side bands resulting from the modulation are opposite in phase to the two voice and single interference side bands in the second amplifying channel; combining the locally modulated carrier with the received modulated carrier and single side band in the second amplifying channel whereby the voice side bands of said combined modulated carriers are cancelled and the single interference side band of said second amplifying channel cancels one of the interference side bands of the locally modulated carrier leaving the sum of the combined carriers and one interference side band as the output of the second amplifying channel; demodulating the outputs of the two amplifying channels so as to provide interference audio and voice audio in the first amplifying channel and only interference audio in the second amplifying channel; and combining the products of said last named demodulations with the interference audio of one channel opposite in phase to that of the other channel.

4. In a radio receiver for receiving double side band amplitude modulated radio waves, means for eliminating the effect of interference manifested as a single side band frequency for any interference audio component, and which is not coherently related-in the form of a double sideband amplitude modulation-to the carrier of the selected transmission comprising: a first amplifying channel; a second amplifying channel; means for feeding the received energy into said two amplifying channels; means for providing a carrier wave which is a duplicate of the Carrier component of the modulated carrier fed into the second amplifying channel as part of the received energy; means for locally modulating the provided carrier with voice audio and interference audio components of the received energy; means for effecting phase opposition between the Voice side bands and two interference side bands resulting from said modulation (as one factor) and the voice and interference side bands in said second amplifying channel (as the other factor); means for combining the locally modulated carrier with the received modulated carrier and interference side band in said second amplifying channel to effect cancellation of the out-of-phase voice side bands of the combined modulated carriers, and also effect cancellation of the interference side band in said second amplifying channel and one of the two interference side bands of the lo-cally modulated carrier thereby leaving the sum of the combined carriers and said remaining interference side band as the output of the said second channel; means for demodulating the outputs of the two amplifying channels so as to provide interference audio and voice audio in one channel and only interference audio in the other channel; and means for combining the products of said demodulating means with the interference audio of one channel opposite in phase to that of the other.

5. For use with a radio receiver for receiving double side band amplitude modulated radio ference manifested as a single side band frequency for any interference audio component, and which is not coherently related-in the form of double side-band amplitude modulation-to the carrier of the selected transmission comprising: an amplifier; means for connecting the input of said amplifier with the receiver circuit at a point ahead of the detector of the receiver so that said amplifier and the receiver circuit ahead of the detector will constitute two channels for the received energy; means for providing a carrier wave which is a duplicate of the carrier component of the modulated carrier fed into said amplifier as part of the received energy; means for locally modulating the provided carrier with voice audio and interference audio components of the received energy; means for effecting phase opposition between the two voice side bands and two interference side bands resulting from said modulation (as one factor) and the Voice and interference side bands in the energy progressing through said amplifier (as the other factor); means for combining the locally modulated carrier with the output of said amplifier to thereby effect cancellation of the out-of-phase voice side bands of the modulated carriers thus combined, and also effect cancellation of the interference side band in the output of said amplifier and one of the two interference side bands of the locally modulated carrier, thereby leaving the sum of the combined carriers and said remaining interference side band as the nal output of said amplifier; means for demodulating said final output of the amplifier so that only interference audio remains; and means for combining said interference audio with the product of the detector in the receiver in such a manner that the interference audio components thus combined are 180 out of phase and cancel each other.

6. In a radio receiver for receiving double size vband amplitude modulated radio waves, means for eliminating the effect of interference manifested as a single side band frequency for any interference audio component, and which is not coherently related-in the form of double sideband amplitude modulation-to the carrier of the selected transmission comprising: a first amplifying channel; a second amplifying channel; a demodulator; means for feeding the received modulated carrier and accompanying single side band (for each frequency) of the interference t each of said amplifying channels and said demodulator; an oscillator; means for controlling the oscil- 10 lator so that its output is a duplicate of the carrier component of the modulated carrier fed into the two amplifying channels; means for locally modulating the output of the oscillator by voice audio and interference audio components of the modulated carrier fed to said two vamplifying channels; means for effecting phase opposition between the two voice side bands and two interference side bands resulting from said modulation (as one factor) and the voice and interference side bands in one of said two amplifying ychannels (as the other factor); means for combining the locally modulated carrier with the received modulated carrier and interference side band in said mentioned one of the two amplifying channels to effect cancellation of the out-of-phase voice side bands of the combined modulated carriers, and also effect cancellation of the interference side band in said mentioned one of the two amplifying channels and one of the two interference side bands of the locally modulated carrier, thereby leaving the sum of the combined carriers and said remaining interference side band as the nal output of said mentioned one of the two channels; means for demodulating the outputs of the two amplifying channels so as to provide interference audio and voice audio as the final output of one channel and only interference audio as the nal output of the other channel; and means for combining said nal outputs of the two channels with the interference audio of one opposite in phase to that of the other.

ROY B. BULLOCK.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,087,288 Landon July 20, 1937 2,183,714 Franke et al. Dec. 19, 1939 2,192,275 Royer Mar. 5, 1940 2,240,500 Gabrilovitch May 6, 1941 2,246,771. Zuccarello June 24, 1941 2,256,199 Hansell Sept. 16, 1941 2,311,696 Rubin Feb. 23, 1943 OTHER REFERENCES Landon: A Study of the Characteristics of Noise; Proceedings of the Institute of Radio Engineers, of Nov. 1936. 

